Abstract: In order to investigate the cause of antimicrobial activity produced by Lactobacillus casei subsp. rhamnosus LCR 719, the inhibitory activity of LCR 719 culture supernatants in MRS was measured by means of the agar well diffusion system. The concentration of acetic acid increases and then decreases, but the concentration of lactic acid continues to increase during fermentation of LCR 719 in MRS. During the whole fermentation, the molecular ratio between lactic acid and acetic acid increases from 0.28 at 6 h to 2.63 at 60 h. The inhibitory activity is the highest at 37 ℃ for 42 h under initial pH 6.50 anaerobicly in MRS, containing 20.0 g/L glucose, 10 ml/L Tween 80. The inhibitory diameter is 42 mm under these optimal conditions against S. aureus. Also the culture supernatants show good inhibitory activity against B. subtilis, S. typhimurium and have weak inhibitory activity against E. coli and EHEC O157. No inhibitory activity of culture supernatants is observed against yeast. These results show that LCR 719 can be used as a potential protective strain in bio-protective.

Key words: Lactobaacillus casei rhamnosus, HPLC, inhibitory effect, fermentation conditions